Walking N out of Trawsfynydd to the A470, a signed path opposite heads N to meet the road again. A track continues towards the Roman fort of Tomen-y-mur, but a lapse of concentration meant that we lost the correct line at 706383 and had to access the site with an awkward fence crossing. A clear path NE from the site of the fort joins the unfenced byway towards the TV station, and a short climb R gives a view over Llyn yr Oerfel, a pleasant enough spot to eat. The slopes to the NE are pathless but easy, and keeping S of the forest towards the highest ground, the attractive Llyn Craig-y-tan bursts into view. A short climb beyond is the cairn on Foel Fawr, with views to the Lleyn Peninsula and lower hills beneath the extensive mantle of mist shrouding the high tops.

It is an easy walk E through an area of grass and outcrops, skirting to the R of the central bog, an uncharacteristic but colourful expanse of heather with reeds and pools of standing water, more like a failed lake. There are several other pools hereabouts, the first named lake being Llyn y Graig-wen below the slopes of the accompanying summit. Walking down the western shore to the outflow, a short steep climb NE gains the cairn. Across Cwm Cynfal we could see Llyn Morwynion and the foreshortened Llyn y Manod below the mist.

We descended steeply NW to a track along the forest edge, which enters the forest by a reedy stream at 733399 and follows a wide clearing with easy walking, passing a forest stream where we collected good water. At the W end at 719398, we climbed a gate to join another track that descends NE to meet the access track to Coch-gwain at 724408. There is a farm gate and track directly opposite - we went through it to meet the line of the public footpath a little lower down, because the line of the footpath through the dense forest to the E is nonexistent. Fearing the worst, we proceeded NW to the R of the barn and to the forest edge wall. A few yards lower down we found a wall gap with loose wire netting across it, and beyond was a clear path through the trees which followed the mapped line precisely, and led down to a new footbridge over the river, then up to a footpath sign on the metalled byway.

Walking E along Cwm Cynfal and passing L of the buildings of Cwm Farm as directed by a waymark, there is a steep climb L to the valley head and the grand waterfall of Rhaeadr-y-Cwm dramatically appears, tumbling through a series of rocky gorges. This was a different experience from Pistyll Rhyd-y-meinciau on the previous trip, where we could climb intimately alongside the falls and cascades. Today the whole waterfall could be seen from the contouring path along the side of the cwm, and the falls themselves are more spectacular, but intimate contact was out of the question!.

Emerging on the road, there was sunshine at last as we walked E past the seasonal cafe to the footpath sign at 751417. The line of the path looked overgrown and a lot rougher than the surroundings, so we climbed the pathless grassy slopes directly E to Moel Llechwedd-gwyn, with the blue expanse of Llyn y Dywarchen making a superb foreground to the Arenigs beyond. The highest ground hereabouts is somewhat rough and tussocky but we found a good patch of soft grass near the lake for an excellent pitch.

At dawn there was a fairly strong wind and the dense mist mantle had dropped to around 600m but was still above our level. From a tiny cairn near the lake, the next objective was Carnedd Iago. The curved line E and SE on the map clearly suggests a route but there is nothing on the ground that follows it such as a wall or fence, however it turned out to be a natural choice. Walking E there is a faint intermittent path through a boggy area which arrives at a boundary stone with a triangular cross section, the faces bearing inscriptions Caernarfon, Denbigh and something unreadable. The path disappears here but we threaded a line aiming for the forest edge and came upon a rectangular boundary stone. Arriving at the fence corner, there was some rough and wet walking to the start of the trees where easy grass took over again to the summit of Carnedd Iago.

Descending S to the forest corner, we crossed a fence to join the obvious forest road through to the B4391 and turned W to the footpath sign by the Nant y Lladron. The path follows the stream and reaches a forest track junction, where we took a chance and headed W with a view to leaving the forest somewhere at the western edge. The track nears the edge as it fords the Afon Prysor but an exit looked impossible, so we carried on round to the start of a pecked path on the map that leaves the track R (771390). This followed a clearing but the going looked appalling. Again we continued on the track to reach the line of power pylons, which are always cleared for some distance around, and we followed them out of the forest, although the going was very rough with large tussocks and dense grasses.

Easy terrain resumed to Llyn Conglog-mawr, which has a rather desolate feel and the nearby presence of the pylons doesn't help, sunshine and blue water might have improved impressions. By crossing the dividing fence right by the outflow, Llyn Conglog-bach was soon gained, which felt more isolated and pleasant.

Ascending S by the fence, very different terrain was heralded by the purple slopes of Y Garn ahead. On reaching a wall junction, a short sharp climb L gains the main objective Llyn y Garn, a lake we had glimpsed from afar when descending from the Arenigs across the valley, and nestles caldera-like just below the top of the hill. Previous suspicions were confirmed, this must be the best defended lake we have seen. Y Garn is almost solid heather with patches of rocks, very steep on most sides and awkward to access from the others, and very few indeed are the feet that have walked here. From our vantage at the northern end, this lovely lake seemed bigger than expected and the dense heather fell abruptly at the shore in most parts, which would have made a walk around it a lengthy and tiring prospect today. Sunshine would have made the lake and heather really vibrant, but dense grey cloud predominated.

Retreating NE around the shoulder of the hill, we were about to descend to the Nant Bryn-celynog when a thin path appeared in the heather above the stream. We followed this along the valley until it petered out, then descended to the wall and crossed it awkwardly where an infant stream runs through it. Just below we could see a farm gate, and further W the line of the dismantled railway running under a bridge. A few yards to the L of the gate there is an access gap in the fence which brought us to our return route along the old railway trackbed. This is now walkable from Arenig to the road junction E of Trawsfynydd at 718359, except for brief diversions to a road. One such case is where an exit is required at the lane at 728360, forcing us onto the A4212 for the rest of the way, however we then noticed that the track is open to walkers at the W end with ladder stiles in place, so it should have been possible to rejoin the track somewhere between those points - maybe via the bridleway at 725360?. The lane from the trackbed end gives a quiet walk back to Trawsfynydd away from the main road.